Wireless computing platforms (or computing platforms) may communicate using one or more wireless communication channels. With today's wireless platforms it is not possible to completely avoid platform radio frequency interference (RFI). Platform components typically include clocks that, during operation, may generate harmonics that overlap with the frequency range of at least one wireless (radio) channel. In some platforms, the close proximity of the clocks and wireless transceivers may introduce significant RFI with one or more wireless channels. The effect of the RFI may be to significantly reduce the data rate and/or operating range of the wireless channel.
Some computing platforms use spread spectrum clock (SSC) modulation to minimize electromagnetic emissions and ease compliance with regional electromagnetic interference (EMI) regulations. For example, FIG. 1A is a graph showing the spectrum of a harmonic near a WiFi 2.5 GHz band of an un-spread 100 MHz clock (e.g., used to generate a PCI Express clock on the platform). FIG. 1C is a plot showing the spectrum of the same harmonic after 1% of conventional triangular center-spread SSC modulation is applied. (FIG. 1B shows one cycle of a typical spread spectrum clocking profile with 1% peak-to-peak amplitude and 30 KHz frequency.) Also shown in FIG. 1C is a particular WiMax channel.
SSC implementations generally reduce the peak electromagnetic energy to attain EMI compliance by spreading energy across adjacent frequencies. As seen in FIG. 1C, the peak energy has been reduced, but the energy has been spread into a WiMax channel, along with adjacent WiFi channels. So, while such SSC modulation can redress EMI issues, unfortunately, the energy is often spread into sensitive areas used by platform radios to receive information. Since platform radios are typically sensitive to noise levels below EMI limits (typically 30 to 40 dB more sensitive), this behavior can seriously degrade radio performance.
Accordingly, a new approach for impeding wireless interference while being able to maintain EMI compliance, if possible, is needed.